1. Field of the Invention
The present invention relates to a refrigeration cycle system having the function of a hot gas heater using a first heat exchanger (evaporator) as a gas refrigerant heat radiator by introducing the refrigerant gas (hot gas) discharged from a compressor directly into the first heat exchanger in heating mode, or in particular to a refrigeration cycle system suitably used with, for example, an automotive air-conditioning system for controlling the refrigerant recovery mode to recover the refrigerant (including oil) staying dormant in a second heat exchanger (condenser) into the first heat exchanger.
2. Description of the Related Art
In the conventional automotive air-conditioning system, hot water (engine cooling water) is circulated in a heating heat exchanger during the winter season, so that the air-conditioning air is heated by the heating heat exchanger with the hot water as a heat source. In the case where the hot water is low in temperature, however, the temperature of the air blown into the compartment is so low that the required heating ability may sometimes not be secured.
In view of this, a refrigeration cycle system capable of exhibiting the heating function using a hot gas heater cycle has been proposed. In this conventional system, in the case where the hot water temperature is lower than a predetermined temperature as at the time of starting the engine, the gas refrigerant discharged from the compressor (hot gas) is introduced directly into the first heat exchanger bypassing the second heat exchanger, so that heat is radiated from the gas refrigerant into the air-conditioning air in the first heat exchanger to exhibit the heating function.
In the automotive refrigeration cycle system, both the second heat exchanger and the compressor are mounted in the engine compartment, or the like, outside the passenger compartment. Once the refrigeration cycle is stopped in winter, for example, the temperature of the second heat exchanger drops to as low as the external air temperature and assumes the lowest temperature in the refrigeration cycle. Thus, the refrigerant saturation pressure of the second heat exchanger assumes the lowest pressure of the refrigeration cycle, thereby posing the problem that the refrigerant enters a dormant state in the second heat exchanger during the winter season when the refrigeration cycle is suspended.
Even after starting the hot gas heater cycle, the refrigerant circulates bypassing the second heat exchanger, and therefore the dormant state of the refrigerant in the second heat exchanger is maintained also after the hot gas heater cycle starts. As a result, during the execution of the hot gas heater cycle, the refrigerant amount in the hot gas heater cycle runs short for a reduced heating performance, thereby inconveniently hampering the smooth return of oil to the compressor.
Japanese Unexamined Patent Publication No. 2000-219033 discloses a system in which the cooling mode is started before the hot gas heater cycle thereby to start the mode of recovering the dormant refrigerant, and upon lapse of a predetermined time, the cooling mode is ended and switched to the heating mode with the hot gas heater cycle.
The same publication also proposes another example of the mode of recovering the dormant refrigerant, in which both the inlet side of the second heat exchanger and the inlet side of the hot gas bypass of the hot gas heater cycle are closed, and the compressor is activated to recover the dormant refrigerant in the second heat exchanger.
In the refrigerant cycle system for automotive vehicles, a variable displacement type refrigerant compressor of swash plate type is used to reduce the drive power of the compressor by reducing the discharge capacity of the compressor under low cooling load. In the variable displacement type refrigerant compressor of a swash plate type, the swash plate chamber accommodating the swash plate communicates with the discharge side and the suction side of the compressor, and the pressure of the swash plate chamber (control pressure) is controlled by a pressure control valve utilizing the difference between discharge pressure and suction pressure. By controlling the pressure of the swash plate chamber, the inclination angle of the swash plate is changed thereby to change the piston stroke and hence the discharge capacity.
In the case where the refrigeration cycle is stopped when the temperature is very low and the hot gas heater cycle is required, for example, when the external air temperature is as low as −20° C. to −30° C., however, the compressor is exposed to the external low temperature environment and its temperature is reduced to as low as the external air temperature. As a result, a great amount of the refrigerant in liquid phase stays in the swash plate chamber of the compressor. Thus, the agitation resistance of the liquid refrigerant greatly increases against the swash plate at the next time of starting the compressor. At the same time, the liquid refrigerant in the swash plate chamber is evaporated to prevent the pressure in the swash plate chamber from being decreased, thereby leading to the unfavorable situation in which the inclination angle of the swash plate cannot be changed rapidly to the large capacity side.
As a result, the compressor cannot be rapidly increased to large discharge capacity. The compressor, if it starts, therefore, operates with a smaller capacity (small piston stroke) for a prolonged time during which the refrigerant is not discharged substantially. During this time, the dormant refrigerant in the second heat exchanger substantially cannot be recovered.
Also, as long as the external temperature remains very low, the refrigerant sealed in the cycle is liquefied and the saturation pressure becomes very low. Thus, the density of the suction refrigerant is very low at the time of starting the compressor. This leads to be the suction refrigerant thin in the compressor and to reduce a flow rate (mass flow rate) of the suction refrigerant, and the discharge pressure of the compressor is not easily increased. As a result, the difference between the discharge pressure and the suction pressure is not readily increased. Even in the case where the liquid refrigerant is not stagnant in the swash plate chamber at the time of starting the compressor, therefore, the inclination angle of the swash plate cannot be rapidly changed to the large capacity side. Thus, even in the case where the compressor is started in a cooling mode, the dormant refrigerant substantially cannot be recovered as in the case described above.
In the prior art disclosed in Japanese Unexamined Patent Publication No. 2000-219033, the mode of recovering the dormant refrigerant is terminated upon the lapse of a predetermined time after starting the recovery mode. In the case where the time set for recovery mode is short as compared with the time when the compressor operates with small capacity after starting, therefore, the dormant refrigerant substantially cannot be recovered even if the recovery mode is executed.
In the case where the recovery mode is set to an excessively long time as compared with the time during which the compressor operates with small capacity, on the other hand, the recovery mode is continued even after the successful recovery of the dormant refrigerant, thereby making it impossible to exhibit the timely heating function due to the hot gas heater cycle.